Facile method for constructing an effective electron transfer mediating layer using ferrocene-containing multifunctional redox copolymer

Our study focused on the formation of an electrochemically active layer on an indium tin oxide (ITO) electrode using a ferrocene-containing multifunctional redox copolymer synthesized by radical polymerization. The copolymer plays four important roles as follows: the surface adhesive monomer acts as an anchor to the ITO surface, the polyethylene glycol (PEG) group prevents nonspecific binding of unwanted biomolecules, the epoxide functional group selectively conjugates antibodies on the polymeric ITO surface, and the ferrocene group is the redox-active compound involved in the electrochemical response. The structure and molecular weight of the polymer were analyzed by nuclear magnetic resonance spectroscopy and gel permeation chromatography, respectively. The thickness, elemental composition, and wettability of the polymer adhesion layer were confirmed by using a surface profiler, an X-ray photoelectron spectrometer, and a contact angle analyzer. The polymer-coated ITO electrodes showed a very high level of antibiofouling effect because of PEG, as compared with the uncoated ITO electrodes (control). Through a microcontact printing method, the antibody was selectively immobilized onto the polymer-coated ITO electrode. The electrochemical response of the polymer-modified ITO electrode was also characterized. The ferrocene-containing polymer exclusively produced a distinguishing redox wave due to ferrocene, as opposed to the ferrocene-free polymer. To further demonstrate the usefulness of our polymer systems, we configured a sandwich immunoassay; the ferrocene-containing polymer largely improved the sensitivity and dynamic range of the immunoassay as compared to the ferrocene-free polymer.